Indirect realism is broadly equivalent to the accepted view of perception in natural science that states that we do not and cannot perceive the external world as it really is but know only our ideas and interpretations of the way the world is.[4]Representationalism is one of the key assumptions of cognitivism in psychology. The representational realist would deny that "first-hand knowledge" is a coherent concept, since knowledge is always via some means. Our ideas of the world are interpretations of sensory input derived from an external world that is real (unlike the standpoint of idealism, which holds that only ideas are real, but mind-independent things are not).

The main alternative to representationalism is anti-representationalism, the view according to which perception is not a process of constructing internal representations.

Primary qualities are qualities which are "explanatorily basic" – which is to say, they can be referred to as the explanation for other qualities or phenomena without requiring explanation themselves – and they are distinct in that our sensory experience of them resembles them in reality. (For example, one perceives an object as spherical precisely because of the way the atoms of the sphere are arranged.) Primary qualities cannot be removed by either thought or physical action, and include mass, movement, and, controversially, solidity (although later proponents of the distinction between primary and secondary qualities usually discount solidity).

Secondary qualities are qualities which one's experience does not directly resemble; for example, when one sees an object as red, the sensation of seeing redness is not produced by some quality of redness in the object, but by the arrangement of atoms on the surface of the object which reflects and absorbs light in a particular way. Secondary qualities include colour, smell, and taste.

However, epistemological dualism has come under sustained attack by other contemporary philosophers, such as Ludwig Wittgenstein (the private language argument) and Wilfrid Sellars in his seminal essay "Empiricism and the Philosophy of Mind". Indirect realism is argued to be problematical because of Ryle's regress and the homunculus argument. Recently, reliance on the private language argument and the "homunculus objection" has itself come under attack. It can be argued that those who argue for "inner presence", to use Antti Revonsuo's term,[22] are not proposing a private "referent", with the application of language to it being "private" and thus unshareable, but a private use of public language. There is no doubt that each of us has a private understanding of public language, a notion that has been experimentally supported;[23]George Steiner refers to our personal use of language as an "idiolect", one particular to ourselves in its detail.[24] The question has to be put how a collective use of language can go on when, not only do we have differing understandings of the words we use, but our sensory registrations differ.[25]

Problems with the indirect theory

A problem with representationalism is that if simple data flow and information processing is assumed then something in the brain must be interpreting incoming data as a "percept". This something is often described as a homunculus, although the term homunculus is also used to imply an entity that creates a continual regress, and this need not be implied. This suggests that some phenomenon other than simple data flow and information processing is involved in perception. This is more of an issue now than it was for rationalist philosophers prior to Newton, such as Descartes, for whom physical processes were poorly defined. Descartes held that there is a "homunculus" in the form of the soul, belonging to a form of natural substance known as res cogitans that obeyed different laws from those obeyed by solid matter (res extensa). Although Descartes' duality of natural substances may have echoes in modern physics (Bose and Fermi statistics) no agreed account of 'interpretation' has been formulated. Thus representationalism remains an incomplete description of perception. Aristotle realized this and simply proposed that ideas themselves (representations) must be aware—in other words that there is no further transfer of sense impressions beyond ideas.

The representational theory of perception

A potential difficulty with representational realism is that, if we only have knowledge of representations of the world, how can we know that they resemble in any significant way the objects to which they are supposed to correspond? Any creature with a representation in its brain would need to interact with the objects that are represented to identify them with the representation. This difficulty would seem reasonably to be covered by the learning by exploration of the world that goes on throughout life. However, there may still be a concern that if the external world is only to be inferred, its 'true likeness' might be quite different from our idea of it. The representational realist would answer to this that "true likeness" is an intuitive concept that falls in the face of logic, since a likeness must always depend on the way in which something is considered.

A semantic difficulty may arise when considering reference in representationalism. If a person says "I see the Eiffel Tower" at a time when they are indeed looking at the Eiffel Tower, to what does the term "Eiffel Tower" refer? The direct realist might say that in the representational account people do not really see the tower but rather 'see' the representation. However, this is a distortion of the meaning of the word see which the representationalist does not imply. For the representationalist the statement refers to the Eiffel Tower, which implicitly is experienced in the form of a representation. The representationalist does not imply that when a person refers to the Eiffel Tower, they are referring to their sense experience, and when another person refers to the Tower, they are referring to their sense experience.

Furthermore, representative realism claims that we perceive our perceptual intermediaries-we can attend to them-just as we observe our image in a mirror. However, as we can scientifically verify, this is clearly not true of the physiological components of the perceptual process. This also brings up the problem of dualism and its relation to representative realism, concerning the incongruous marriage of the metaphysical and the physical.

The new objection to the Homunculus Argument claims that it relies on a naive view of sensation. Because the eyes respond to light rays is no reason for supposing that the visual field requires eyes to see it. Visual sensation (the argument can be extrapolated to the other senses) bears no direct resemblance to the light rays at the retina, nor to the character of what they are reflected from or pass through or what was glowing at the origin of them. The reason given is that they only bear the similarities of co-variation with what arrives at the retinas.[26] Just as the currents in a wire going to a loudspeaker vary proportionately with the sounds that emanate from it but have no other likeness, so too does sensation vary proportionately (and not necessarily directly) with what causes it but bears no other resemblance to the input. This implies that the colour we experience is actually a cortical occurrence, and that light rays and external surfaces are not themselves coloured. The proportional variations with which cortical colour changes are there in the external world, but not colour as we experience it. Contrary to what Gilbert Ryle believed, those who argue for sensations being brain processes do not have to hold that there is a "picture" in the brain since this is impossible according to this theory since actual pictures in the external world are not coloured.[27] It is plain that Ryle unthinkingly carried over what the eyes do to the nature of sensation; A. J. Ayer at the time described Ryle's position as "very weak".[28] So there is no "screen" in front of cortical "eyes", no mental objects before one. As Thomas Hobbes put it: "How do we take notice of sense?—by sense itself". Moreland Perkins has characterized it thus: that sensing is not like kicking a ball, but rather "kicking a kick".[29] Today there are still philosophers arguing for colour being a property of external surfaces, light sources, etc.[30]

A more fundamental criticism is implied in theories of this type. The differences at the sensory and perceptual levels between agents require that some means of ensuring at least a partial correlation can be achieved that allows the updatings involved in communication to take place. The process in an informative statement begins with the parties hypothetically assuming that they are referring to the "same" entity or "property", even though their selections from their sensory fields cannot match; we can call this mutually imagined projection the "logical subject" of the statement. The speaker then produces the logical predicate which effects the proposed updating of the "referent". If the statement goes through, the hearer will now have a different percept and concept of the "referent"—perhaps even seeing it now as two things and not one. The radical conclusion is that we are premature in conceiving of the external as already sorted into singular "objects" in the first place, since we only need to behave as if they are already logically singular.[31] The diagram at the beginning of this entry would thus be thought of as a false picture of the actual case, since to draw "an" object as already selected from the real is only to treat the practically needful, but strictly false, hypothesis of objects-as-logically-singular as ontologically given. The proponents of this view thus argue that there is no need actually to believe in the singularity of an object since we can manage perfectly well by mutually imagining that 'it' is singular. A proponent of this theory can thus ask the direct realist feels why he or she thinks it is necessary to move to taking the imagining of singularity for real when there is no practical difference in the outcome in action. Therefore, although there are selections from our sensory fields which for the time being we treat as if they were objects, they are only provisional, open to corrections at any time, and, hence, far from being direct representations of pre-existing singularities, they retain an experimental character. Virtual constructs or no, they remain, however, selections that are causally linked to the real and can surprise us at any time—which removes any danger of solipsism in this theory. This approach dovetails with the philosophy known as social constructivism.[32]

The character of experience of a physical object can be altered in major ways by changes in the conditions of perception or of the relevant sense-organs and the resulting neurophysiological processes, without change in the external physical object that initiates this process and that may seem to be depicted by the experience. Conversely any process that yields the same sensory/neural results will yield the same perceptual experience, no matter what the physical object that initiated the process may have been like. Furthermore, the causal process that intervenes between the external object and the perceptual experience takes time, so that the character of the experience reflects, at the most, an earlier stage of that object than the one existing at the moment of perception. As in observations of astronomical objects the external object may have ceased to exist long before the experience occurs. These facts are claimed to point to the conclusion that the direct object of experience is an entity produced at the end of this causal process, distinct from any physical object that initiates the process."[33]

The adverbial theory

The above argument invites the conclusion of a perceptual dualism that raises the issue of how and whether the object can be known by experience. The adverbial theory proposes "that this dualism is a dualism of objects, with perceptual experience being a more direct experience of objects of a different sort, sense-data."[33] Perceptual dualism implies:

both an act of awareness (or apprehension) and an object (the sense-datum) which that act apprehends or is an awareness of. The fundamental idea of the adverbial theory, in contrast, is that there is no need for such objects and the problems that they bring with them (such as whether they are physical or mental or somehow neither). Instead, it is suggested, merely the occurrence of a mental act or mental state with its own intrinsic character is enough to account for the character of immediate experience.[33]

According to the adverbial theory, when, for example, I experience a silver elliptical shape (as when viewing a coin from an angle) I am in a certain specific state of sensing or sensory awareness or of being appeared to: I sense in a certain manner or am appeared to in a certain way, and that specific manner of sensing or of being appeared to accounts for the content of my experience: I am in a certain distinctive sort of experiential state. There need be no object or entity of any sort that is literally silver and elliptical in the material world or in the mind. I experience a silver and elliptical shape because an object or entity that literally has that color and shape is directly before my mind. But the nature of these entities and the way in which they are related to the mind are difficult to understand. The adverbial theory has the advantage of being metaphysically simpler, avoiding issues about the nature of sense-data, but we gain no real understanding of the nature of the states in question or of how exactly they account for the character of immediate experience."[33]

Arguments against direct realism

The argument from illusion

Illusion creates a problem for naïve realists as it suggests our senses are fallible, perceiving things that aren't there. In this illusion, the lines are horizontal, despite how they appear.

This argument was "first offered in a more or less fully explicit form in Berkeley (1713)."[33] It is also referred to as the problem of conflicting appearances (e.g. Myles Burnyeat's article Conflicting Appearances). It has been argued that "informed commonsense" indicates that perceptions often depend on organs of perception.[34] For example, humans would receive visual information very differently if they, like flies, had compound eyes, and may not even be able to imagine how things would appear with entirely different sense organs such as infra-red detectors or echo-location devices. Furthermore, perception systems can misrepresent objects even when in full working order, as shown, for example, by optical illusions like the Müller-Lyer illusion. More dramatically, sometimes people perceive things which are not there at all, which can be termed instances of "hallucination" or "perceptual delusion".[34]

Illusions are present in nature. Rainbows are an example of a perceptual delusion. "For, unlike an architectural arch, a rainbow recedes as we approach it, never to be reached."[35]

The argument from illusion allegedly shows the need to posit sense-data as the immediate objects of perception. In cases of illusion or hallucination, the object has qualities that no public physical object in that situation has and so must be distinct from any such object.[33] Naïve realism may accommodate these facts as they stand by virtue of its very vagueness (or "open-texture"): it is not specific or detailed enough to be refuted by such cases.[34] A more developed direct realist might respond by showing that various cases of misperception, failed perception, and perceptual relativity do not make it necessary to suppose that sense-data exist. When a stick submerged in water looks bent a direct realist is not compelled to say the stick actually is bent but can say that the stick can have more than one appearance: a straight stick can look bent when light reflected from the stick arrives at one's eye in a crooked pattern, but this appearance is not necessarily a sense-datum in the mind. Similar things can be said about the coin which appears circular from one vantage point and oval-shaped from another. Pressing on your eyeball with a finger creates double vision but assuming the existence of two sense-data is unnecessary: the direct realist can say that they have two eyes, each giving them a different view of the world. Usually the eyes are focused in the same direction; but sometimes they are not.

However, this response is presumably based on previously observed data. If one were to be able to observe nothing other than the stick in the water, with no previous information, it would appear that the stick was bent. Visual depth in particular is a set of inferences, not an actual experience of the space between things in a radial direction outward from the observation point.[36] If all empirical evidence is based upon observation then the entire developed memory and knowledge of every perception and of each sense may be as skewed as the bent stick. Since objects with different qualities are experienced from each of the different perspectives there is no apparent experiential basis for regarding one out of any such set of related perceptual experiences as the one in which the relevant physical object is itself immediately experienced. The most reasonable conclusion is that the experienced object is always distinct from the physical object or at least that there is no way to identify which, if any, of the immediately experienced objects is the physical object itself. Epistemologically it is as though physical objects were never given, whether or not that is in fact the case.[33]

Another potential counter-example involves vivid hallucinations: phantom elephants, for instance, might be interpreted as sense-data. A direct realist response would differentiate hallucination from genuine perception: no perception of elephants is going on, only the different and related mental process of hallucination. However, if there are visual images when we hallucinate it seems reasonable that there are visual images when we see. Similarly if dreaming involves visual and auditory images in our minds it seems reasonable to think there are visual and auditory images, or sense-data, when we are awake and perceiving things. This argument has been challenged in a number of different ways. First it has been questioned whether there must be some object present that actually has the experienced qualities, which would then seemingly have to be something like a sense-datum. Why couldn't it be that the perceiver is simply in a state of seeming to experience such an object without any object actually being present? Second, in cases of illusion and perceptual relativity there is an object present which is simply misperceived, usually in readily explainable ways, and no need to suppose that an additional object is also involved. Third, the last part of the perceptual relativity version of the argument has been challenged by questioning whether there is really no experiential difference between veridical and non-veridical perception; and by arguing that even if sense-data are experienced in non-veridical cases and even if the difference between veridical and non-veridical cases is, as claimed, experientially indiscernible, there is still no reason to think that sense-data are the immediate objects of experience in veridical cases. Fourth, do sense-data exist through time or are they momentary? Can they exist when not being perceived? Are they public or private? Can they be themselves misperceived? Do they exist in minds or are they extra-mental, even if not physical? On the basis of the intractability of these questions, it has been argued that the conclusion of the argument from illusion is unacceptable or even unintelligible, even in the absence of a clear diagnosis of exactly where and how it goes wrong.[33]

Direct realists can potentially deny the existence of any such thing as a mental image but this is difficult to maintain, since we seem able to visually imagine all sorts of things with ease. Even if perception does not involve images other mental processes like imagination certainly seem to. One view, similar to Reid's, is that we do have images of various sorts in our minds when we perceive, dream, hallucinate and imagine but when we actually perceive things, our sensations cannot be considered objects of perception or attention. The only objects of perception are external objects. Even if perception is accompanied by images, or sensations, it is wrong to say we perceive sensations. Direct realism defines perception as perception of external objects where an "external object" is allowed to be a photon in the eye but not an impulse in a nerve leading from the eye. Recent work in neuroscience suggests a shared ontology for perception, imagination and dreaming, with similar areas of brain being used for all of these.

^Hearing (or audition) is the ability to perceive (create ideas of)sound by detecting vibrations. The sound waves of language cannot perceive directly. They are only heard, interpreted and understood because the physical waves were transformed into ideas (Mental representation of sound wages) by our brains.

^ abBernecker, S. (2008). The Metaphysics of Memory. Philosophical Studies Series. Springer. p. 62. ISBN 9781402082191. LCCN2008921236. The distinction between direct and indirect realism about perception has an interesting history. There was a time when perception was understood to be of things themselves, not of our ideas of things. This is what we find in Aristotle and Aquinas, who maintain that the mind or understanding grasps the form of the material object without the matter. What we perceive directly, on this view, are material objects. This changed in the seventeenth century with Descartes and Locke. who can be read as saying that the primary objects of perception are not things external to the mind but sense-data. Sense-data are the messengers that stand between us and physical objects such as tables and chairs. While indirect realism was the standard view of early modern philosophers, nowadays direct realism is, once again, in fashion.

^Tom Rockmore, Before and After Hegel: A Historical Introduction to Hegel's Thought, Hackett Publishing, 2003, p. xviii: "Hegel follows Kant ... in limiting claims to know to the empirically real. In short, he adopts a view very similar to Kant's empirical realism."

^Samuel Lebens, Bertrand Russell and the Nature of Propositions: A History and Defence of the Multiple Relation Theory of Judgement, Routledge, 2017, p. 34.

Discordianism is a paradigm based upon the book Principia Discordia, written by Greg Hill with Kerry Wendell Thornley in 1963, the two working under the pseudonyms Malaclypse the Younger and Omar Khayyam Ravenhurst. According to self-proclaimed "crackpot historian" Adam Gorightly, Discordianism was founded as a parody religion. Many outside observers still regard Discordianism as a parody religion, although some of its adherents may utilize it as a legitimate religion or as a metaphor for a governing philosophy.The Principia Discordia, if read literally, encourages the worship of the Greek goddess Eris, known in Latin as Discordia, the goddess of disorder, or archetypes and ideals associated with her. Depending on the version of Discordianism, Eris might be considered the goddess exclusively of disorder or the goddess of disorder and chaos. Both views are supported by the Principia Discordia. The Principia Discordia holds three core principles: the Aneristic (order), the Eristic (disorder), and the notion that both are mere illusions. Due to these principles, a Discordian believes there is no distinction between disorder and chaos, since the only difference between the two is that one refers to 'order'. This is likely a major reason for the inconsistency in the wording. An argument presented by the text is that it is only by rejecting these principles that you can truly perceive reality as it is, chaos.

It is difficult to estimate the number of Discordians because they are not required to hold Discordianism as their only belief system, and because, by nature of the system itself, there is an encouragement to form schisms and cabals.

Hallucinatory realism is a term that has been used with various definitions since at least the 1970s by critics in describing works of art. In some occurrences the term has had connections to the concept of magical realism, although hallucinatory realism is usually more specific to a dream-state. The term occurs in the motivation for Mo Yan's Nobel Prize in Literature.

The map–territory relation describes the relationship between an object and a representation of that object, as in the relation between a geographical territory and a map of it. Polish-American scientist and philosopher Alfred Korzybski remarked that "the map is not the territory" and that "the word is not the thing", encapsulating his view that an abstraction derived from something, or a reaction to it, is not the thing itself. Korzybski held that many people do confuse maps with territories, that is, confuse models of reality with reality itself. The relationship has also been expressed in other terms, such as Alan Watts's "The menu is not the meal."

In philosophy of mind, naïve realism, also known as direct realism, common sense realism or perceptual realism, is the idea that the senses provide us with direct awareness of objects as they really are. Objects obey the laws of physics and retain all their properties whether or not there is anyone to observe them. They are composed of matter, occupy space and have properties, such as size, shape, texture, smell, taste and colour, that are usually perceived correctly.

In contrast, some forms of idealism claim that no world exists apart from mind-dependent ideas, and some forms of skepticism say we cannot trust our senses. Naïve realism is known as direct as against indirect or representational realism when its arguments are developed to counter the latter position, also known as epistemological dualism; that our conscious experience is not of the real world but of an internal representation of the world.

Neopragmatism, sometimes called post-Deweyan pragmatism, linguistic pragmatism, or analytic pragmatism, is the philosophical tradition that infers that the meaning of words is a function of how they are used, rather than the meaning of what people intend for them to describe.

The Blackwell Dictionary of Western Philosophy (2004) defines "neo-pragmatism" as "A postmodern version of pragmatism developed by the American philosopher Richard Rorty and drawing inspiration from authors such as John Dewey, Martin Heidegger, Wilfrid Sellars, W. V. O. Quine, and Jacques Derrida". It's a contemporary term for a philosophy which reintroduces many concepts from pragmatism. While traditional pragmatism focuses on experience, Rorty centers on language. The self is regarded as a "centerless web of beliefs and desires".

It repudiates the notions of universal truth, epistemological foundationalism, representationalism, and epistemic objectivity. It is a nominalist approach that denies that natural kinds and linguistic entities have substantive ontological implications. Rorty denies that the subject-matter of the human sciences can be studied in the same ways as we study the natural sciences.It has been associated with a variety of other thinkers including Hilary Putnam, W. V. O. Quine, and Donald Davidson, though none of these figures have called themselves "neopragmatists". The following contemporary philosophers are also often considered to be neopragmatists: Nicholas Rescher (a proponent of methodological pragmatism and pragmatic idealism), Jürgen Habermas, Susan Haack, Robert Brandom, and Cornel West.

Objectivism is a philosophical system developed by Russian-American writer Ayn Rand. Rand first expressed Objectivism in her fiction, most notably The Fountainhead (1943) and Atlas Shrugged (1957), and later in non-fiction essays and books. Leonard Peikoff, a professional philosopher and Rand's designated intellectual heir, later gave it a more formal structure. Rand described Objectivism as "the concept of man as a heroic being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute". Peikoff characterizes Objectivism as a "closed system" that is not subject to change.Objectivism's central tenets are that reality exists independently of consciousness, that human beings have direct contact with reality through sense perception (see Direct and indirect realism), that one can attain objective knowledge from perception through the process of concept formation and inductive logic, that the proper moral purpose of one's life is the pursuit of one's own happiness (see Rational egoism), that the only social system consistent with this morality is one that displays full respect for individual rights embodied in laissez-faire capitalism, and that the role of art in human life is to transform humans' metaphysical ideas by selective reproduction of reality into a physical form—a work of art—that one can comprehend and to which one can respond emotionally.

Academic philosophers have mostly ignored or rejected Rand's philosophy. Nonetheless, Objectivism has been a significant influence among right-libertarians and American conservatives. The Objectivist movement, which Rand founded, attempts to spread her ideas to the public and in academic settings.

The philosophy of perception is concerned with the nature of perceptual experience and the status of perceptual data, in particular how they relate to beliefs about, or knowledge of, the world. Any explicit account of perception requires a commitment to one of a variety of ontological or metaphysical views. Philosophers distinguish internalist accounts, which assume that perceptions of objects, and knowledge or beliefs about them, are aspects of an individual's mind, and externalist accounts, which state that they constitute real aspects of the world external to the individual. The position of naïve realism—the 'everyday' impression of physical objects constituting what is perceived—is to some extent contradicted by the occurrence of perceptual illusions and hallucinations and the relativity of perceptual experience as well as certain insights in science. Realist conceptions include phenomenalism and direct and indirect realism. Anti-realist conceptions include idealism and skepticism.

Right-libertarianism, or right-wing libertarianism, refers to libertarian political philosophies that advocate natural law and a major reversal of the modern welfare state. Right-libertarians strongly support private property rights and defend market distribution of natural resources and private property. This position is contrasted with that of some versions of left-libertarianism.Right-libertarian political thought is characterized by the strict priority given to liberty, with the need to maximize the realm of individual freedom and minimize the scope of public authority. Right-libertarians typically see the state as the principal threat to liberty. This anti-statism, however, differs from anarchist doctrines in that it is based upon an uncompromising individualism that places little or no emphasis upon human sociability or cooperation.The philosophy is also rooted in the ideas of individual rights and laissez-faire economics. The right-libertarianism theory of individual rights generally stresses that the individual is the owner of their person and thus that people have an absolute entitlement to the property that their labor produces. Economically, right libertarians emphasize the self-regulating nature and mechanisms of the market, portraying government intervention and attempts to redistribute wealth as invariably unnecessary and counter-productive. Although all right-libertarians oppose government intervention, there is a division between those who adhere to the anarcho-capitalism position, who view the state as an unnecessary evil, and minarchists who recognize the necessary need for a minimal state.Although influenced by classical liberal thought, with some viewing right-libertarianism as an outgrowth or as a variant of it, there are significant differences. With Edwin van de Haar stating that "confusingly, in the United States the term libertarianism is sometimes also used for or by classical liberals. But this erroneously masks the differences between them." Classical liberalism refuses to give priority to liberty over order and therefore does not exhibit the hostility to the state, which is the defining feature of libertarianism. Subsequently, right-libertarians believe classical liberals favor too much state involvement, arguing that they do not have enough respect for individual property rights and lack sufficient trust in the workings of the free market and spontaneous order leading to support of a much larger state. Also, Right-libertarians often attack classical liberals for their support for central banks and monetarist policies.

In the philosophy of language, the distinction between sense and reference was an innovation of the German philosopher and mathematician Gottlob Frege in 1892 (in his paper "On Sense and Reference"; German: "Über Sinn und Bedeutung"), reflecting the two ways he believed a singular term may have meaning.

The reference (or "referent"; Bedeutung) of a proper name is the object it means or indicates (bedeuten), its sense (Sinn) is what the name expresses. The reference of a sentence is its truth value, its sense is the thought that it expresses. Frege justified the distinction in a number of ways.

Sense is something possessed by a name, whether or not it has a reference. For example, the name "Odysseus" is intelligible, and therefore has a sense, even though there is no individual object (its reference) to which the name corresponds.

The sense of different names is different, even when their reference is the same. Frege argued that if an identity statement such as "Hesperus is the same planet as Phosphorus" is to be informative, the proper names flanking the identity sign must have a different meaning or sense. But clearly, if the statement is true, they must have the same reference. The sense is a 'mode of presentation', which serves to illuminate only a single aspect of the referent.Much of analytic philosophy is traceable to Frege's philosophy of language. Frege's views on logic (i.e., his idea that some parts of speech are complete by themselves, and are analogous to the arguments of a mathematical function) led to his views on a theory of reference.

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